Nearly a third of the world’s economic output will come from countries facing “high” to “extreme” risks from the impacts of climate change within 12 years, according to a new report.

The Climate Change Vulnerability Index, an annual report produced by UK-based risk analysis firm Maplecroft, found that climate change “may pose a serious obstacle to sustainable economic growth in the world’s most commercially important cities.”

The index ranked the vulnerability of the world’s countries, and the 50 cities deemed most economically important, to the impacts of climate change, by evaluating their risk of exposure to extreme climate events, the sensitivity of their populations to that exposure and the adaptive capacity of governments to respond to the challenge.

Five cities at ‘extreme risk’

1. Dhaka 2. Mumbai 3. Manila 4. Kolkata 5. Bangkok

It said the combined GDP of the 67 countries classed as facing “high” or “extreme” risks was projected to nearly triple from $15 trillion to $44 trillion by 2025 — meaning nearly a third of the global economy would be coming under increasing threat from extreme climate-related events. It projected the population of those countries — currently estimated at more than 4.5 billion — could exceed 5 billion by 2025.

The index’s findings bore particularly bad news for Bangladesh, which topped both lists, with its capital, Dhaka, ranked the most vulnerable city due to its exposure to threats such as flooding, storm surge, cyclones and landslides, its susceptible population and weak institutional capacity to address the problem.

Along with the Bangladeshi capital, the four other cities categorized as facing “extreme risk” from climate change impacts were also located in Asia — Mumbai, Manila, Kolkata and Bangkok — and projected to be centers of high economic growth.

“The combined GDP in these cities is forecast to almost triple from US$275 billion to US$804 billion by 2025, representing the greatest combined growth in any of the risk categories,” said the report, released Wednesday. The figures, it said, underlined the way in which “cities with some of the biggest economic growth potential are among those with the greatest vulnerability to climate change.”

Greenpeace’s chief scientist Doug Parr said the report highlighted “just how urgent the need is for the international community to tackle climate change.” “Without a binding global agreement the economic and social impact of global warming will be devastating,” he said.

“It would be morally negligent for countries with large emissions to ignore the mounting evidence of the impact global warming that shows that some of the poorest nations on the planet will be hit hardest, while those nations who are seeing the first signs of economic growth after years of stagnation will see those gains washed away by consequences of global warming.”